The invention relates to a device for producing a drilled hole with an undercut.
Devices for producing drilled holes with undercuts are known. In one such device a drilling tool-holder is engaged in and provided with a rotatable sleeve with a connecting pipe for supplying cooling and flushing liquid and a drilling tool is held in the drilling tool-holder. The drilling tool has a drilling head faced with diamond chips and the sleeve has an axial throughgoing bore in which the drilling tool-holder engage the drilling tool.
To produce an undercut in a drilled hole, a drill with a hard metal drill bit that has lateral cutting edges projecting at the drilling head can be used. The undercut is produced by pivoting the drilling tool, once the cylindrical part of the drilled hole has been made, and in this position performing one or more stirring movements with the drilling machine. In the bottom part of the drilled hole, the drilling head reams out an undercut into which an expansible plug with an expansible sleeve which fits the undercut can be inserted and installed. To facilitate the pivoting movement of the drilling tool, the drilling tool is provided with a fixed stop collar, which, to form a pivot bearing, is supported in a depression of a stop plate positioned on the concrete surface.
In high-strength concrete, and especially in reinforced concrete, because of the high wear rate and risk of breakage, a drilling tool with a hard metal bit is not very suitable for producing drilled holes. It is therefore usual to use diamond-faced bits on such building materials to drill holes. A drilled hole with an undercut is then produced in two steps. In the first step, the cylindrical drilled hole is made with a diamond crown bit and the drilled core remaining after drilling is broken away. The undercut is then produced with a reaming apparatus. Because the core does not always break off right at the depth that the crown bit has reached, to avoid damaging the reaming apparatus the undercut is made at a distance from the bottom of the drilled hole. In addition to two working steps to produce the drilled hole with an undercut, a cylindrical drill hole that is deeper than would actually be required for anchoring the fixing element is also always necessary.